The present invention pertains generally to the control of the acceleration pulse delivered by HYGE (Hydraulically Controlled, Gas Energized) crash simulation sleds used in safety testing of vehicle components.
The HYGE (Hydraulically Controlled, Gas Energized) system derives its powerful thrust force from an actuator assembly 1 which uses differential gas pressure acting on the two faces of a thrust piston 10 in a closed cylinder 12, as shown in FIG. 1. The cylinder is separated into two chambers A, B by an orifice plate 14. A relatively low gas pressure in chamber A, known as the Set Cylinder, forces the thrust piston 10 against a seal ring 16 on the orifice plate 17. The area of the entire thrust piston face is exposed to the gas pressure in chamber A, defined by floating pistons 26 opposed to thrust piston 10. On the other side of the piston, only the small area within the seal is exposed, through the orifice opening, to the gas pressure in chamber B, known as the Load Cylinder, in which a floating piston 24 is located.
In preparation for firing, compressed gas is introduced into the Load Cylinder until the forces on the thrust piston 10 are equalized. To fire the piston, a small burst of compressed gas is introduced into the trigger chamber 18, which is the small area within the seal on the chamber B side of the piston. This burst upsets the equilibrium, opening the seal at the orifice plate 17 and exposing the entire surface area of the piston to the the seal at the orifice plate 17 and exposing the entire surface area of the piston to the higher pressure in the Load Cylinder. This results in a powerful thrust force being applied to the thrust piston in the direction of chamber A. This thrust force is then transmitted to a crash sled through the thrust column 20.
The thrust force has, until now, been controlled by regulating the compressed gas flow through the orifice plate by the shape of the metering pin 22, which is progressively drawn through the orifice as the metering pin, thrust piston, and thrust column assembly move in the direction of chamber A during the firing event.
The HYGE (Hydraulically Controlled, Gas Energized) reaction simulates the longitudinal deceleration conditions of an impact, but in reverse. Prior to an actual crash, the test vehicle and test dummies each move at a constant velocity. At impact, they are stopped very rapidly. During a HYGE (Hydraulically Controlled, Gas Energized) crash simulation sled test, the test vehicle and dummies, which are attached to the sled, are initially at zero velocity. This situation simulates the constant velocity condition prior to an actual crash. The metering pin programmed acceleration of the HYGE (Hydraulically Controlled, Gas Energized) sled drives an automobile assembly attached to the crash sled, which is shown in FIG. 2, out from under the test dummies, producing a response similar to that caused by the rapid deceleration of a moving vehicle. The acceleration and deceleration effects are interchangeable because the accelerationxe2x80x94time relationships are the same in both cases.
The metering pin controlled force output works well, but is cumbersome and time-consuming to change to another forcexe2x80x94time profile, requiring disassembly of the Set and Load Cylinders and removal and insertion of a different-shaped metering pin. A large inventory of such metering pins may be required in order to represent all the forcexe2x80x94time shapes required.
Control of the forcexe2x80x94time relationship during actuator motion is possible by other means than just metering pin shape. Instead of allowing all the force applied to the thrust piston to be directly applied to the thrust column and then used to accelerate the sled, an electronically controlled force control device may be employed to control the amount of force being made available to accelerate the sled.
Such an acceleration control (accelerator) device may take the form of a brake or force actuator acting in parallel with the HYGE (Hydraulically Controlled, Gas Energized) actuator to provide a force-path to ground either in parallel with the sled, or a force generator/absorber in parallel with the HYGE (Hydraulically Controlled, Gas Energized) actuator. This parallel accelerator device is to be closed-loop controlled using sled acceleration as the feedback signal source to compare with the desired acceleration value at a sequence of time increments and to apply a corresponding acceleration output to the sled or HYGE (Hydraulically Controlled, Gas Energized) actuator to drive the acceleration error (difference between desired and actual acceleration) toward zero, thus achieving true closed-loop control over the accelerationxe2x80x94time pulse during the actuator firing event.